It's the TTL connector on an MFJ-1270. The pins are 1/10" spacing, but I don't know what it's called so I can order another one.
It's called a 0.1" pin header. Okay, yes, it's a specific connector from AMP or Berg or Molex or someone that we could probably identify if we put our minds to it, and if you used the exact match it would fit those latches or keys or whatever they are... but if all you want is to build a cable and be able to plug it into the TNC, then pretty much anything described as "single-row 0.1-inch female" will work, like this kind of header (you can snip it to the correct length, and solder to the back), or this kind of connector, commonly called DuPont. The second kind is nicer, but you need a crimping tool to attach the female contact to your wire, before pushing it into the plastic housing. Either one should slide onto the pins on the TNC without interference — you'll just have to be careful to plug it in the right way :)